Foot-and-mouth disease is a dangerous, international epizootic disease which causes the most serious injury to livestock. This is widely prevailing all over the world, for example, in Asia, middle East, Africa and South America except only some regions. Fortunately, at present, it is free in Japan. However, if once invaded, the eradication of the disease will be difficult since it is extremely strongly infectious, and if the worst comes to the worst, the disease will prove to be the deathblow to the internal livestock industry.
Foot-and-mouth disease (FMD) is a viral infectious disease, and the FMD virus causing the disease includes seven serotypes while the existence of more than 60 sub-types of the virus is known. The blood of the animal as infected with such FMD viruses shall have antibodies to the virus-constituting proteins, which are produced in the blood in accordance with numerous different types of viral mutation. Therefore, when the presence or absence of the FMD viral infection is diagnosed (judged) in animals, it is often impossible to serologically detect FMD viruses of different serotypes.
On the other hand, the FMD virus comprises a number of non-structural proteins such as typically RNA-dependent RNA polymerase which produces its own gene, and many of such non-structural proteins are common to all serotypes of FMD viruses. When a recent new vaccine as purified to a high degree is administered to an animal, almost no antibody to non-structural proteins is produced in the blood of the animal but, in fact, the existence of the antibodies to non-structural proteins in the blood of the FMD-infected animal is significantly recognized.
For these reasons, in order to diagnose the presence or absence of infection with FMD viruses in animals, it is considered extremely important to detect the antibodies specific to the non-structural proteins (3D;RNA polymerase, 3C;protease, L;protease, and other 2A, 2B, 2C, 3A and 3B proteins) existing in the blood samples collected from the animals to be tested.
Up to this time, various methods for diagnosis of FMD viral infections using, as the antigen the RNA polymerase site of 3D protein have been attempted by many scientists.
However, in the reaction systems having a relatively high detection sensitivity, such as enzyme-linked immunosorbent assay systems (ELISA), if the site having an amino acid sequence significantly common to that among Picornavirus which is close related to FMD virus is used as the antigen non-specific reactions often occur problematically.
In addition, it is said in the reports that have heretofore been made, that the reactivity of the 3D protein site with infected positive sera is not so good.
Given the situation, if a high-sensitivity method of detecting antibodies specific to only non-structural proteins, while being not accompanied by any non-specific reactions, is developed, it becomes possible to easily select and differentiate naturally-infected, antibody-positive animals from the group of vaccine-dosed, antibody-positive animals. Accordingly, it will be possible to provide a means of preventing FMD from invading FMD-free countries such as Japan and also to provide for FMD-infected countries an extremely valuable technique of applying vaccines to animals to thereby reduce the FMD-infected regions in the countries and even an extremely valuable technique of diagnosis of FMD in animals to thereby exterminate FMD in the FMD-infected countries.